Pump and motor hydraulic transmission system



Jan. 2, 1951 F. B. LEVETUS EI'AL 2,536,558

PUMP AND MOTOR HYDRAULIC TRANSMISSION SYSTEM Filed Jan. 2, 1947INVENTORS FRANCIS B. Lav ETUS GEORGE E.CHITTENDEN Patented Jan. 2, 1951PUMP AND MOTOR HYDRAULIC TRANSMISSION SYSTEM Francis Benjamin Levetusand George Edward Chittenden, Coventry, England, assignors to TheKeelavite Company Limited, Coventry, England, a company of Great BritainApplication January 2, 1947, Serial No. 719,824 In Great Britain January4, 1946 7 Claims.

This invention relates to hydraulic power transmission systems of thekind comprising a power-driven pump by which liquid is delivered toperformed by the pump. Such an arrangement considerably relieves thepump especially at low motor speeds and when the motor is stopped, butdoes not deal adequately with, the problem of preventing over-running ofthe motor during transition periods when sudden reductions in load onthe motor or sudden closing of the control valve takes place.

The object of the present invention is to provide an improved hydraulicpower transmission system of the kind referred to in which, as far aspossible, the positive control of the motor speed in accordance with thesetting and changes of setting of the control valve will tend to beachieved at all times.

To this end a hydraulic power transmission system of the kind referredto according to the present invention includes not only a relief valvebetween the pump and motor controlled by the pressure in an operatingchamber connected to a point between the motor and control valve so thatthe control valve opens when this pressure exceeds a predeterminedvalue, but also an automatic braking valve disposed between the controlvalve and the motor and so controlled by the pressure at this point thatit closes if and when such pressure exceeds a predetermined value.

Conveniently, means are provided for adjusting to fine limits therelative pressures at which respectivel the relief valve opens and thebraking valve closes so as to enable the relationship between thesepressures to be adjusted to ensure that the relief valve opens at aslightly lower pressure than that at which the braking valve closeswithout, however, there being any substantial band of pressures overwhich the relief valve and the braking valve are both open so that closecontrol of the motor speed is lost and without therebeing any pressureat which both valves tend to remain closed with the consequent tendencyfor instability of conditions in the system and undesired loading of thepump.

The invention may be carried into practice in various ways, but oneconstruction according to the invention is illustrated, somewhatdiagrammatically by way of example in the accompanying drawing in which-Figure l is a diagrammatic view of a complete hydraulic powertransmission system embodying the invention,

Figure 2 is a vertical cross-section through the relief valve embodiedin the system shown in Figure 1 and I Figure 3 is a similar view toFigure 2 of the braking valve embodied in the system shown in Figure 1.

The system shown in Figure 1 comprises a reservoir A for liquid fromwhich the liquid is drawn through a pipe A by a power-driven pumpindicated at B and delivered via a pipe 13 through a relief valveindicated generally at C and a pipe 0 to a hydraulic motor indicatedgenerally at D from which the liquid returns through a pipe D a brakingvalve E, a pipe E, a control valve F and a pipe G to the reservoir A.

The braking valve E is normally continuously open and control valve Fcontrols the speed of the motor D by controlling the rate at whichliquid is permitted to flow through it and is arranged in known mannerso that for each setting of the valve there will be a correspondingappropriate speed of the motor I) which will tend to be maintained inspite of variations in the load on the motor.

To this end the relief valve C as shown clearly inFigure 2 comprises anoperating piston C mounted to move axially in the casing C and rigidwith the valve member C which controls a relief port C situated at thejunction of the pipes B and C which are in free communication with oneanother.

The underside of the piston C is subject to the pressure in an operatingchamber H which is connected through a pipe H to a point in the pipe Ethat is between the motor D and control valve F. This pressure isopposed on the piston C by a spring C the loading of which can be variedb an adjustment of an adjustable abutment C A passage (3 through thevalve 0 serves to ensure that both ends thereof are subject to reliefpressure only. It will thus be seen that when pressure between the motorD and the control valve F exceeds a predetermined value, the reliefvalve C will be opened against the action of the spring C so as tofacilitate the flow of fluid through the relief port C which isconnected by a return pipe C to the reservoir A. In this way, a constantpressure tends to be maintained in the pipe E on the pressure side ofthe control valve F, and hence a constant flow tends to take placethrough this valve F for any given setting thereof. This operation willbe clear when it is considered that increases in the load on the motorDwill produce a reduction in the pressure in the pipe E and hence on thecontrol valve F and in the chamber H This reduction in pressure causes'a closing movement of the valve C which will thereby increase thepressure of fiuidsupplied;

to the motor D to a degree sufficient to meet the increased load andrestore thezpressure in the pipe E and hence in the chamber H Thechamber H ma also be connected through a spring-pressed valve J to apoint in the pipe B between the pump B and the relief valve C, whilea'restriction indicated at H is provided in the pipe H so that if andwhen excess pressure occurs in the pipe'B the valve J will lift topermit flow therethrough in excess of that which the restriction canaccommodate thus producing increased pressure in the chamber H whichwill cause the relief valve C to lift. The valve J is set so that itopens only if an excessive pressure greater than the maxi mum at whichthe apparatus is designed to operate occurs in the pipe B this valvethus being :in-the nature of a safety valve.

The braking .valve E is as shown, arranged between'the motor D and thecontrol valve F so "that all liquid passing through the pipes D Ebetween the motor D and the control valve-F has topass through thebraking valve.

This valve, which as mentioned above is normally continuously open,comprises a casing E containing an axially movable valve member E'adapted to control the outlet port E and provided with a piston E onwhich acts a spring E tending to maintain the valve open so that freeflow of fluid can take place between the pipes D and E Thevalve member Eis provided with a bore E so that an operating chamber E above-thepiston E is subject normally at all times-to the pressure in the pipes DE The space E below the piston communicates through a port E and pipe Econtaining a restriction E with the reservoir A.

It-will be seen that the braking valve will normally be maintained openby the spring E but that if and when the pressure in the pipes D Eexceeds a predetermined value, this pressure,

I acting on the top of the piston E will cause the valve to close andthus prevent flow of liquid through the pipe D If desired, a point inthe pipe D ma be connected through a spring pressed safety valve K tothe chamber E through the part of the pipe E on the adjacent side of therestriction E The valve K is then arranged so as to open only if andwhen a pressure occurs in the pipe D in excess of the maximum for whichthe apparatus is designed.

It will be seen that with this arrangement, should such an excessivepressure be experienced, the valve K will open so that pressure isadmitted to the chamber E to open the braking valve. In

:addition, a spring pressed safety valve L may 'be provided in parallelwith the control valve F, this safety valve also being adapted to openonly on the occurrence of a pressure thereon in excess of the maximumfor which theiapparatus is designed.

'liquid from the motorja relief val-ve situated be- ;tween the pump andmotor and-including means tending to close the relief-valve and-anoperating pipesD E remains substantially constant, as

willnormally be-the case, the braking valve E remainsopen. If, however,in these circumstances, .the' pressure in the pipes D E shows an-appreciable increase above that at which the relief valveC opens, asmay occur for example due'tosuddn removal of the load on the motor D, orto the fact that the motor is suddenly driven forexamp1e by the fallingof a hammer or other member which it operates, the braking valve E willatonce close and-thus. positively prevent'the speeding up of the motorD. It will thus be seen that thespeed-of the motor D is positivelycontrolled under substantially all conditions.

What we claim as our invention and desire .to secure by Letters Patentis:

1. A hydraulic power transmission system including in combination apower driven-pump, a

hydraulic motor to which liquid isdelivered by the pump, acontrolvalvecontrolling the flow of liquid from the motor, a relief valvesituatedbetween the pump and'motor and including means tending to close therelief valve and an operating member disposed in an operating chamberthe pressure in which acts on the operating member totend to 1 open thevalvefmeansfor connecting 'the'operating chamber to -aipoint between themotor and' the control valve, and an automatic braking valve disposedbetween 'the motor Y and the control valve and 'inoludirig means'tending to open-the brakingvalve, 'an" op'er'ating member disposed in anoperatingchamber the pressure in which acts on theoperating-memberin adirectionto close- -the braking 'valve and means con- Y necting theoperating -'-chambr of" the braking valve to a point between themotorand the tontrolvalve.

2. A hydraulic power transmission system'ineluding in combination a--power driven pump-a hydraulic motor to which liquid is delivered by thepump, a controlvalvecontrolling the flow of member disposedinan'operating chamber the pressure in which acts on the operating-memberto' tend to open the-valve, means for connecting theoperatingchamber toa-point between the 'motor and the control valve, an automatic'brakingvalve disposed between the motor and the control 'valveand including-means tending to open the braking valve," an operating member'disposedin an operating chamber the pressure in j which acts on the operatingmember -in' a direc- 'tion to close the-braking valvepmeans'connectmgthe operating chamber of the braking valve to'a point between the motorand the cdntrofvalve,

-and means for adjustin'g- 'within fine limits the relative-pressures at"which respectively the relief valve is opened and the brakingvalvecloses.

3. A- hydr'aul'ic power-transmission system in- 'cluding' in combinationa hydraulic pump; a hydraulic motor having its inlet connected to theoutlet from the pump, a'control"va1ve1 controlling the fibW oi -fluidthrough the outlet ffromx the motor. a relief valve situated between thepump and the motor and. comprising a valve member, a spring tending tomaintain the valve closed, an operating chamber and a piston in theoperating chamber connected to the valve so as to open the valve whenthe pressure in the operating chamber exceeds a predetermined value,means for connecting the operating chamber to a point between the motorand the control valve, an automatic braking valve disposed between thecontrol valve and the motor and comprising a valve member, a springtending to maintain the valve open, an operating chamber and a piston inthe operating chamber adapted to close the valve when the pressure inthe operating chamber exceeds a predetermined value, and meansconnecting the operating chamber of the braking valve to 'a pointbetween the motor and the control valve.

4. A hydraulic power transmission system including in combination ahydraulic pump, a hydraulic motor having its inlet connected to theoutlet from the pump, a control valve connected to the outlet from themotor for controlling the flow of fluid through the motor, a reliefvalve in the connection between the pump and the motor and comprising avalve member, a counterbalancing spring tending to maintain the valveclosed, an operating chamber and a piston in the operating chamberconnected to the valve so as to open the valve when the pressure in theoperating chamber exceeds a predetermined value, fluid pressureconducting means connecting the operating chamber to a point in theconnection between the motor and the control valve, an automatic brakingvalve in the connection between the control valve and the motor andcomprising a valve member, a counterbalancing spring tending to maintainthe braking valve open, an operating chamber having fluid pressureconducting means between it and the connection from the motor to thecontrol valve, a piston in the operating chamber adapted to close thebraking valve when the pressure in the operating chamber exceeds apredetermined value, and means for varying the relative forces of thecounterbalancing springs acting on the pistons respectively of therelief valve and braking valve to enable the pressures at which thesevalves respectively open and close to be adjusted in relation to oneanother so that the relief valve opens at a slightly lower pressure thanthat at which the braking valve closes whereby the speed of the motor isautomatically controlled.

5. A hydraulic power transmission system including in combination theelements set forth in claim 3 in which a spring pressed pilot valve issituated between the pump and the relief valve and arranged when openedto deliver liquid under pressure to the operating chamber of the reliefvalve, and a restriction is provided between this operating chamber andthe point in the connection between the motor and the control valve towhich it is connected.

6. A hydraulic power transmission system including in combination theelements set forth in claim 3 in which a point between the motor and thecontrol valve is connected through a spring pressed pilot valve to achamber in which lies the face of the piston of the braking valve remotefrom the operating chamber of the braking valve so that when this pilotvalve opens it admits pressure tending to open the braking valve.

7. A hydraulic power transmission system including the elements claimedin claim 4 in which a spring pressed pilot valve is situated between thepump and the relief valve and arranged when opened to deliver liquidunder pressure to the operating chamber of the relief valve, and arestriction is provided between this operating chamber and the point inthe connection between the motor and the control valve to which it isconnected; and a point in the connection between the motor and thebraking valve is connected through a second spring pressed pilot valveto a chamber in which lies the face of the piston of the braking valveremote from the operating chamber of the braking valve so that when thispilot valve opens it admits pressure tending to open the braking valve.

FRANCIS BENJAMIN LEVETUS. GEORGE EDWARD CHITTENDEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,005,731 Elrnst et a1 June 25,1935 2,005,732 Ernst et al June 25, 1935 2,157,240 Keel May 9, 19392,166,940 Conradson July 25, 1939 2,272,684 Vickers Feb. 10, 1942

